Tuneups

The timing on new cars, or anything made in roughly the past 20 to 25 years, is generally not adjustable. There is a crank sensor that senses TDC and the computer sets the timing. The only way to adjust it would be to fabricate a new mount for the sensor so you could move it from where the computer thinks it is. Many cars have a knock sensor which adjusts the timing on the fly to make sure the engine doesn't ping/knock.

A tune up today is basically plugs and if needed, plug wires. My pt calls for new plugs every 30K and new wires every 60K.

I still like to check it with a light every year or so just to make sure it looks nice and stable and isn't bouncing around. You can't adjust the timing, but you can estimate the amount of timing jitter there is and know when you're heading for mechanical issues.

It only takes a minute to do, you might as well do it while you're doing plugs and filters anyway.

Don't forget air filter, fuel filter, and maybe cabin air filter. It's also an opportunity to check all the hoses and belts, look for bad seals.

Don't forget to change your differential and transmission fluid according to the severe service schedule in the owner's manual also!

--scott

I have Iridium plugs which should last 75 - 100 k miles.

Cabin air filter does not affect engine performance.

Andy

Might affect your performance though! :)

When the cabin filter in my car clogged up it started drawing air in through the drain tube when on recirc. The a/c water had no where to go except on the passenger floor.

That's no reason to neglect it. New windshield wipers too.

--scott

add in a timing belt and water pump on some engines. Plus a coolant flush/refill, check of the power steering fluid and testing brake fluid for water absorption level.

Yep they can spot a lot of problems before you can even tell it's an issue. GM for one turns on the light if the cam crank correlation changes by more than 4 degrees on some engines. Others are a bit looser but not by much.

I do not know under what conditions the CEL comes on; surely it varies by manufacturer to an extent.

Years ago some of the spark plug wires on my 1992 Mercury Grand Marquis had gone bad. This manifested as rough idle and loss of power, presumably from cylinders misfiring.

I can't seem to recall the CEL being lit at any time before I fixed the problem. I only knew there was a problem, because I could feel and hear the rough running.

Maybe I'm misremembering though.

Fortunately, the fix was very affordable and easy: new spark plug wiring harnesses, which cost all of maybe $40 total to do both sides, and took about 15 minutes to install.

92 would have been OBD I, very few real sensors at that time. These days the ECM and other modules monitor everything.

Yeah, my 92 explorer had some problem spark plugs and missed badly and the CEL never came on. Must be too old a system.

Anecdotally, it seems as if CELs light up most often when there's some problem with the emission control system. Or the engine computer thinks there is.

Often, you can get away with driving around with a lit CEL for quite a while, as it doesn't immediately affect driveability.

According to this article on the topic:

CEL on some cars will come on if you have a loose/leaky gas cap. How does the engine computer even know? Wow.

Just realized I've never had the CEL turn on, since I started driving the car 131000 miles ago. I don't even know what it looks like.

Youtube Homemade smoker for engine vacuum hoses ...I am going to make one.

The EVAP tests on modern vehicles can detect VERY small leaks. It actually is a simple system.

During "normal operation there is a vent that allows air to move in/out of the tank. Needed because the pressure differential needs to be kept low.

The system tests under specific circumstances. You basically have two methods, pressure and vacuum. The vacuum system is the most common.

Engine or pump vacuum is used along with 2-3 solenoid valves, a pressure sensor and the EVAP map in the ECM. The test is - Turn off the external vent. Open the vacuum solenoid so vacuum can enter the tank. Now count how long it takes to achieve a certain vacuum level in the tank. Compare that to the map table. IF the numbers match within a certain percentage for the fuel level and outside temperature and engine RPM. You're OK and get no light.

Next the system will count how long it takes for that vacuum level to remain steady and only drop a set percentage to account for fuel use and vapor pressure.

If the drop is within the table limits you're OK and get no light.

The system then returns to the open vent and closed vacuum solenoid.

The systems that show "check gas cap" lights do the same tests, but they also factor in the fuel levels from the last time the engine was shut off. So you pull into the gas station, fill the tank, forget to put the cap on or tighten it down and start down the road. The ECM runs the EVAP cycle and says OOPS we have a BIG leak. Looks at the last EVAP cycle and sees that it passed. It then looks at the fuel level and finds the level went from 12% to 99%. This triggers a "Pending" code for the large leak BUT the ECM will turn on the idiot light telling you to check the gas cap. You get out, install the cap fully, and continue on. Now the next time the EVAP test runs it sees the pending code. If the test passes that code is erased and you're ok. If however the test fails the light comes on.

How big of a leak does the system look for?

Well on the early OBD II (1995-1999) systems you had two levels, one was a "gross leak" aka fuel cap, and what was considered a "large leak" was .040"

The standards were changed in 2000 and from 2000-2014 the systems will trigger at a leak of .020"

That standard has also been lowered and the current "small leak" level detects a leak down to .010"

Pretty good explanation with pictures.

I have a homebrew and a commercial machine. Use both quite a bit.